How to round the inner corners of an MDF box
We have reached the step of rounding the inner corners of our MDF nightstand boxes. Usually, the inner corners are not fully visible if the furniture has drawers installed. It would be enough to round the first few centimeters, to get a uniform front edge. But, if the bottom drawer is missing the solution with the first centimeters is no longer a good one. An example is an old project, a bathroom cabinet for the washbasin. The bottom drawer is missing, and that area looks very well due to the rounded inner corners.
For our nightstands, even if we used drawers at the bottom, we rounded the entire inner corners.
This method is part of a nightstand “how to” video. You can find it on our YouTube channel:
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Using our nightstand box from the step where we have already glued the additional strip and we drew the semicircles, in order to round the corners, we used:
- a chisel and a hammer
- a narrow belt sander
- a piece of round rod as sandpaper holder
1. The first thing we did was to remove as much material as possible out of the added strip, taking care not to cut too much (not to exceed the drawn circle).
We positioned the chisel on the edge of the strip, in an upright position, and I tapped lightly with the hammer to remove thin bands of MDF. To make sure we wouldn’t cut too much material, we only cut the first half of the added strip. We didn’t continue any longer, because of the chisel handle. We couldn’t position the chisel vertically. The blade would have been tilted towards the inside of the corner and we would have cut too much.
2. We turned the box over and we did the same thing with the second half.
3. We used the narrow belt sander to round as much as possible. It is not the best sander (it is a no-name one), but it is extremely useful for the hard to sand areas. The roller at the end of the sander belt had a radius slightly smaller than the the one we wanted to get. So, we had to be careful not to sand too much and to follow constantly the drawn semicircles.
For this step, we used a shop vacuum (Karcher WD 3) to quickly remove the dust resulting while sanding.
4. At the end we used a piece of round rod (35 mm in diameter) as sandpaper holder to evenly sand the inner corner along its entire length. This step takes time. We first used 80 grit sandpaper to reduce the sanding time, then we continued with 120 grit sandpaper to get a smoother surface.
If small unevenness appear, the edges break, or too much material is sanded, we can correct them with wood putty, but only after properly removing all the MDF dust. After the putty dries, the surface has to be sanded again with 120 grit sandpaper (using the same round piece of wood as support).